JP-A-2013-107624 discloses a seat driving device that selectively actuates a plurality of position adjusting mechanisms by a single driving motor. The seat driving device is configured to perform four position adjustments (adjustments of a seat in a front and rear direction and an upper and lower direction, reclining angle adjustment of a seat back and tilt angle adjustment of a seat cushion) by using the single driving motor. Therefore, a clutch mechanism is respectively provided in a path for distributing an output of the driving motor to each position adjusting mechanism. The clutch corresponding to a mechanism that performs the position adjustment is caused to come into a connection state, so that the output of the driving motor is transmitted to the corresponding position adjusting mechanism. On the other hand, the clutches corresponding to mechanisms that do not perform the position adjustment are caused to come into a disconnection state, so that the output of the driving motor is not transmitted to the corresponding position adjusting mechanisms.
Use frequencies are different between the plurality of position adjusting mechanisms. For example, the adjustment of the seat in the front and rear direction may be more frequently used than the other adjustments, depending on usage of the seat. The seat driving device is required to secure predetermined durability, irrespective of the use frequency. In the seat driving device, it is the clutch mechanism that highly affects the durability, depending on the difference of the use frequency.
Therefore, in the seat driving device, the clutch mechanisms are designed so that a problem does not occur as to the durability of the clutch mechanism of the position adjusting mechanism of which the use frequency is high. As a result, excessive quality is secured for the clutch mechanisms of the position adjusting mechanisms of which the use frequency is low. Therefore, the cost increases due to the excessive quality. It is considered to make the durability of each clutch mechanism different, in correspondence to the use frequency. In this case, however, it is not possible to commonalize each clutch mechanism, so that the cost increases.